A print showing letters, numbers, figures and the like is normally formed on a surface of a printing object such as a CD (compact disk), a CD-R (recordable CD) or a normal paper with water-based ink by an ink-jet printing method or the like.
However, since the aforementioned print is formed by printing with water-based ink, when the surface of the print gets wet with water, the water-based ink flows easily, causing illegible letters, numbers, figures, etc. and disappearance thereof.
As a method for improving the water resisting property of such a water-based ink print, there is a method in which resin solution including organic solvent and synthetic resin dissolved therein is applied to the surface of the print by a bar coater or the like and then dried to thereby form a protective coat thereon. However, the method had a drawback that the drying rate of the solvent was slow. Furthermore, the water resisting property was insufficient, and therefore the further improvement of the water resisting property was required. That is, although the print may not be completely disappeared, the print tends to become blurry or illegible.
In some CD-Rs, a commercially available print seal is adhered on an upper surface of a CD-R via an adhesive layer of the print seal and a print is formed on the seal with water-based ink. In this case, there are drawbacks that the water resisting property is insufficient and that the adhesive contained in the adhesive layer permeates the information storage medium as a substrate material and finally reaches the recording layer as the core of the information storage medium, which causes disappearance of the recorded information.
On the other hand, in a magnetic-stripe card used as a credit card, a cash card or the like, it is common that the card is embossed with personal information such as an individual name and a registration number so that the information protrudes on the card surface. However, in a recently proposed notable card-shaped optical disk having the same size as that of a card such as a credit card or a business card, a recording layer is formed on approximately the entire surface of the disk. Therefore, it is impossible to employ the aforementioned embossing processing in order to form the aforementioned personal information on the optical disk. Furthermore, in a conventional card with embossed portions showing personal information such as an individual name or a registration number, there is a problem that the embossed portions become bulky when a plurality of cards are stored in a wallet, a card case or the like in piles. Thus, the inventors tried to print personal information such as an individual name or a registration number with oil-based ink on a first printed layer of oil-based ink formed on a surface of a card-type optical disk by a sublimation hot-printing method or the like. This revealed that there was the following problem. Although the information was clearly printed, the print was not fixed well on the first printed layer of oil-based ink and therefore the print was easily disappeared when the print was touched or rubbed with a hand.
The present invention was made in view of the aforementioned technical background. The present invention aims to provide a protective agent for a print capable of effectively preventing the print from wearing off and excellent in quick-drying property and therefore the solvent does not reach a substrate material (printing object) on which the print is formed, which in turn can prevent bad influence on the substrate material. The present invention also aims to provide a method of forming a protective layer for the print and an information storage medium with a well-fixed print that does not become bulky even if they are stored in piles.
Other objects of the present invention will be apparent from the following embodiments.